I. Field of the Invention
The present invention relates to powder material compacting methods and, more particularly, to an improved method for compacting powder material into spherical and similar shapes.
II. Description of the Prior Art
The present invention is concerned with a method using improved tooling for use in powder-compacting presses such as are disclosed in U.S. Pat. Nos. 3,826,599; 3,775,032; 3,730,659; 3,726,622; 3,645,658; 3,574,892; 3,561,056; 3,415,142; 3,344,213; and 3,328,840, all of which are assigned to the same assignee as the present application.
In the powder-compacting presses disclosed in the aforementioned U.S. patents, the articles are compacted and formed in a multi-cavity die forming part of a punch and die set, with the finished articles being automatically ejected from the die cavities, picked up by a vacuum pick-up head, and conveyed into suitable receptacles. A work station positioner assembly, which is part of the press, is mounted angularly movable transversely over the die plate and carries a powder dispenser, an anvil and the pick-up head. The powder dispenser, which is supplied with powder from a primary powder supply means connected thereto by means of a flexible tubing or the like, is first positioned over the die cavity or cavities which are thus filled with powder as the punches are displaced downwardly so as to draw a predetermined amount of powder into the die cavity or cavities. The dispenser is then removed from above the die cavity or cavities by the subsequent angular motion of the station positioner assembly, and the anvil is, in turn, positioned over the die cavities. The anvil is clamped over the die cavity by means of a pivotable clamp supported above the anvil and actuated in timed relation with the movement of the punches. The anvil is held down with sufficient pressure to permit the compaction of the powder against the anvil as a result of an upward motion of the punches into the die cavity or cavities. The anvil is then removed from its position over the die cavity or cavities and is replaced by the pick-up head by a further angular motion of the work station positioner transversely across the face of the die plate. The punches are displaced upwardly so as to bring their upper ends in substantial flush alignment with the upper surface of the die plate, such that the finished compacted articles are ejected from the die cavities and picked up by the pick-up head. As the result of a return angular motion of the work station positioner to the initial fill position, the pick-up head is removed from over the die cavity and is disposed over one or, if a plurality of die cavities are employed, a series of discharge apertures arranged in a disposition similar to the arrangement of the die cavities in the die plate, and the finished compacted article or articles are drawn, as by vacuum, through the discharge aperture or apertures into a container or separate containers.
The tooling used in the prior art in compacting powder materials into spherical forms consists of a die having a center bore, and upper and lower punches the faces of which define a spherical cavity. Typically, powder material is charged in a measured quantity into the die bore and hemispherical cavity of the lower punch. The upper punch is then moved through the bore and compacts the powder material in the spherical cavity defined by the end faces of upper and lower punches. It is necessary to make the ends of the walls of the punch members thick enough at the equator of the spherical cavity to prevent distortion or breakage of the walls by the compacting forces. As a result, a portion of the powder material is squeezed in the equatorial space and the end faces of the punches do not make contact with each other. The compacted material then has an equatorial ring or bulge of greater diameter than the diameter of the spherical cavity. The excess material in this ring has to be removed by a tumbling or similar process in order to obtain a spherical article.
The present invention provides a method for producing a compacted spherical article without an equatorial ring or bulge.